The combination of sunshine and England's progress in the World Cup means the
country is in a very optimistic mood, says Dr Cliff Arnall, of the University of
Cardiff.

He has devised a formula for measuring mood through outdoor activity, energy
levels and sunlight. He used a similar method to calculate that Jan 23 was the
most depressing day.

His formula is O + (N x S) + Cpm/T + He, in which O stands for being outdoors
and outdoor activity, N for nature, S for social interaction, Cpm for childhood
summers and positive memories, T for temperature and He for holidays and
anticipating time off.

Today was pinpointed as the happiest day of the year because of its added
"thank goodness it's Friday" feeling at the start of a summer weekend.